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Grade 12 Physics entrance exam, 2013 E.C. (2021)

Real questions from the Grade 12 university entrance exam in Physics, as students sat it in 2013 E.C. Every question comes with the correct answer and a worked explanation.

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  • Natural science stream

    Who sits it

  • 2013 E.C. (2021)

    Exam year

  • 48 questions with answers

    In this set

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Answer each question yourself before opening the answer. The explanations point to the exact place in the textbook, so you know which page to reread when you miss one.

Question 1

According to the kinetic theory of gases, the

  1. A.particles of an ideal gas undergo inelastic collision between themselves and with the walls of the container.
  2. B.diffusion rate of a gas is inversely proportional to the square root of the molar mass because it is directly proportional to the molecular speed.
  3. C.internal energy of an ideal gas is equal to the potential energy due to interaction between the particles of the gas.
  4. D.average translational kinetic energy of the particles of an ideal gas increases as the gas gets cooled.
Show the answer and explanation

Answer: B diffusion rate of a gas is inversely proportional to the square root of the molar mass because it is directly proportional to the molecular speed.

Why

According to Graham's law, the rate of diffusion of a gas is inversely proportional to the square root of its molar mass. This is because the root-mean-square speed of the gas molecules, vrms=3RT/Mv_{rms} = \sqrt{3RT/M}, is also inversely proportional to the square root of the molar mass.

Question 2

At t=0t = 0, an object undergoing SHM has maximum displacement of 0.650 m and angular frequency of 7.40 rad/s. Which of the following is correct about the motion of the oscillator?

  1. A.The position of the object is x=0.650cos⁡(7.40t)x = 0.650\cos(7.40t) and its acceleration is a=−35.59cos⁡(7.40t)a = -35.59\cos(7.40t).
  2. B.The frequency of the oscillator is 7.40 Hz and its period is 0.135 s.
  3. C.The position of the object is x=0.650sin⁡(7.40t)x = 0.650\sin(7.40t) and its velocity is v=4.81cos⁡(7.40t)v = 4.81\cos(7.40t).
  4. D.The position of the object is x=0.650cos⁡(7.40t)x = 0.650\cos(7.40t) and its acceleration is a=−3.59sin⁡(7.40t)a = -3.59\sin(7.40t).
Show the answer and explanation

Answer: A The position of the object is x=0.650cos⁡(7.40t)x = 0.650\cos(7.40t) and its acceleration is a=−35.59cos⁡(7.40t)a = -35.59\cos(7.40t).

Why

With maximum displacement at t=0t = 0, the position equation is x=Acos⁡(ωt)=0.650cos⁡(7.40t)x = A\cos(\omega t) = 0.650\cos(7.40t). Since acceleration is a=−ω2xa = -\omega^2 x, we have a=−(7.40)2⋅0.650cos⁡(7.40t)=−35.59cos⁡(7.40t)a = -(7.40)^2 \cdot 0.650\cos(7.40t) = -35.59\cos(7.40t).

Question 3

A 0.35 kg mass attached to the end of a spring oscillates 2.5 times per second with amplitude of 0.15 m. Which of the following is true about the motion of the mass?

  1. A.The velocity when it is 0.10 m from equilibrium is 3.0 m/s.
  2. B.The acceleration when it is 0.10 m from equilibrium is 25.00 m/s225.00\ \mathrm{m/s^2}.
  3. C.The velocity when it passes the equilibrium is 2.355 m/s.
  4. D.The total energy of the system is 97.0 J.
Show the answer and explanation

Answer: C The velocity when it passes the equilibrium is 2.355 m/s.

Why

The maximum velocity of the mass occurs when it passes through the equilibrium position, given by vmax=Aω=A(2πf)v_{max} = A\omega = A(2\pi f). Substituting the values with π≈3.14\pi \approx 3.14, we get vmax=0.15×2×3.14×2.5=2.355 m/sv_{max} = 0.15 \times 2 \times 3.14 \times 2.5 = 2.355\text{ m/s}.

Question 4

Identify a true statement about a mechanical wave.

  1. A.The speed of a wave traveling across a thin string is equal to its speed when traveling across a thick string of the same length and tension.
  2. B.The speed of a wave traveling along a string increases as the tension in the string increases and as the linear density of the string decreases.
  3. C.As a wave travels from one point to another along a medium, it transmits energy and particles of the medium from point to point.
  4. D.The velocity of a traveling wave is equal to the velocity of the particles through which the wave propagates.
Show the answer and explanation

Answer: B The speed of a wave traveling along a string increases as the tension in the string increases and as the linear density of the string decreases.

Why

The velocity of a transverse wave on a stretched string is given by v=T/μv = \sqrt{T/\mu}, where TT is the tension and μ\mu is the linear mass density. Therefore, the wave speed increases when tension increases or when the linear density decreases.

Question 5

Which one of the following is a correct statement about the intensity of sound?

  1. A.It is directly proportional to the square of the distance from the sound source.
  2. B.It is inversely proportional to the square of the distance from the source of sound.
  3. C.It is the product of power of a sound and area through which the sound is transmitted
  4. D.It is energy transmitted per unit time.
Show the answer and explanation

Answer: B It is inversely proportional to the square of the distance from the source of sound.

Why

The intensity II of sound from a point source in an open space is given by I=P/(4πr2)I = P / (4\pi r^2), which is inversely proportional to the square of the distance rr from the source.

Question 6

Which of the following is correct about Doppler effect?

  1. A.When a sound source moves away from stationary observer, the frequency detected by the observer increases, whereas the wavelength decreases.
  2. B.Doppler effect is the change in the frequency of a wave due to relative motion between the wave source and an observer.
  3. C.It is the change in the velocity of a wave due to relative motion between the source of the wave and an observer.
  4. D.When a source of sound wave moves toward stationary observer, the wavelength of the wave increases while its frequency decreases.
Show the answer and explanation

Answer: B Doppler effect is the change in the frequency of a wave due to relative motion between the wave source and an observer.

Why

The Doppler effect is defined as the change in the observed frequency of a wave due to the relative motion between the wave source and the observer.

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Physics papers from other years

2018 E.C. (2026)2017 E.C. (2025)2016 E.C. (2024)2015 E.C. (2023)2014 E.C. (2022)2012 E.C. (2020)2011 E.C. (2019)2010 E.C. (2018)2009 E.C. (2017)2008 E.C. (2016)2007 E.C. (2015)2006 E.C. (2014)2005 E.C. (2013)

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Are these the real 2013 E.C. Physics entrance exam questions?

Yes. They come from the national university entrance exam in Physics that students sat in 2013 E.C. (2021). Our set holds 48 of its questions, each with its answer and an explanation that points back to the textbook.

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